In a large saucepan, heat the olive oil over medium heat. Add the zucchini, onions, apples, and carrot and cook without browining until the onion is soft and translucent, about 15 minutes. Add the garlic, ginger, chiles, cilantro stems, and curry paste. Continue cooking, stirring often, until all the ingredients are tender, about 20 minutes.

Add the broth and bring to a boil over high heat. Reduce to a simmer and cook uncovered until the vegetables and the apples begin to fall apart, about 20 minutes. Add the lemon juice and 2 teaspoon salt.

Remove the soup from the heat to cool slightly and then puree in a blender or food processor, or with an immersion blender, until very smooth. Reheat the soup just before serving. Season to taste with salt.